Elastomers and tire with N-alkyl-p-quinonediimino triazine stabilizers

ABSTRACT

Novel N-alkyl-p-quinonediimino triazine compounds are disclosed which are useful as antiozonants for unsaturated high polymers. The compound may be prepared by oxidizing a 2,4,6-tris(N-alkyl-p-phenylenediamino) 1,3,5-triazine with a neutral or basic oxidizing agent and isolating the product.

This is a divisional of application Ser. No. 07/421,438 filed Oct. 13,1989, which has now issued on Jun. 6, 1992 as U.S. Pat. No. 5,118,807.

BACKGROUND OF THE INVENTION

This invention relates to new quinonediimine derivatives of triazinecompounds which are useful as antiozonants for rubber, processes fortheir manufacture, and to their use in inhibiting the deterioratingeffect of ozone on unsaturated polymers. In particular, novelN-alkyl-p-quinonediimino triazine compounds are described.

It is well known that ozone causes surface cracking of conventionalhighly unsaturated rubber vulcanizates when the rubber is placed understrain in an ozone environment. The most severe deterioration occurswhen a small number of cracks are formed which grow rapidly into deep,disruptive fissures. These ozone cracks seriously shorten theserviceable life of the article.

The use of well known paraphenylenediamine materials has improved ozoneprotection under both static and dynamic conditions, however, even thebest of the class have a very strong tendency to both stain anddiscolor. The term "stain" or "staining" is herein used to describe thecharacteristic of a material to diffuse through a polymeric substrateand discolor the adjacent surface. This diffusion staining is highlyobjectionable in most light colored rubber articles. In tires, which isthe largest application in which the ozone protection is required, thetendency to diffusion staining of the aforementionedparaphenylenediamine materials is objectionable particularly in whitesidewall type tires. Even in non-white sidewall type tires, the tendencyof the materials to diffuse to the surface of the tire sidewall can beobjectionable in that a brown or yellow dull surface is created on thetire sidewall. One common term for this phenomena is blooming. This isaesthetically objectionable in that it detracts from the general jetblack, smooth appearance of a new tire. It is obvious that in a whitesidewall tire, the migration of the brown or yellow discoloring materialto the surface of the white sidewall is highly objectionable andgenerally difficult to remove during cleaning of the tire surface.

An object of this invention is to provide an antiozonant material whichis highly effective in protecting the carcass from ozone attack. Afurther object is to provide ozone protection in a static condition atvery low levels and to protect the rubber article during extended agingconditions against ozone attack. Yet another object is to produce acompound which does slowly diffuse and does not produce an objectionablebrown or yellow bloom.

An advantage of the substituted triazine compounds is that it produces asubstantially non-staining antiozonant of high molecular weight. Afurther advantage is that it slowly migrates to the surface of therubber article. Another advantage is that the compounds do not tend toincrease scorchiness of the compounded rubber stock in which it is used.This improves processing safety over other paraphenylenediamineantiozonants.

BRIEF DESCRIPTION OF THE INVENTION

The object and advantages of the invention may be obtained using theessential ingredient of the invention which is a compound of the generalformula: ##STR1## Y and Z are independently selected from ##STR2## R¹,R² and R³ are radicals independently selected from a C₃ -C₁₈ branched orlinear alkyl, or a C₃ -C₁₂ cycloalkyl or a C₃ -C₁₂ cycloalkylsubstituted with one or more C₁ -C₁₂ alkyl groups.

The products may be produced by a process of oxidizing a2,4,6-tris(N-alkyl-p-phenylenediamino 1,3,5-triazine [sometimes referredto hereinafter as triazines or triazine intermediates] in the presenceof an oxidizing agent. These triazines are known and taught in U.S. Pat.Nos. 4,794,135 and 4,794,134 which are incorporated herein by reference.

The novel compounds of the present invention may be prepared by aprocess comprising: reacting an N-alkyl-p-phenylenediamine with atri-halo-triazine in a solvent to form a reaction mixture including a2,4,6-tris (N-alkyl-p-phenylenediamino)-1,3,5-triazine trihydrohalide;and neutralizing said2,4,6-tris(N-alkyl-p-phenylenediamino)-1,3,5-triazine trihydrohalidewith a base to form a2,4,6-tris(N-alkyl-p-phenylenediamino)-1,3,5-triazine;

Oxidizing said 2,4,6-tris(N-alkyl-p-phenylenediamino) 1,3,5-triazine inthe presence of an oxidizing agent.

Unsaturated polymers may be stabilized against ozone degradation byincorporation therein of an effective amount of the novel compounds ofstructure (I).

DETAILED DESCRIPTION OF THE INVENTION

Refering now to structure (I), the preferred compositions are those inwhich R¹, R² and R³ are linear or branched C₃ -C₁₈ alkyl groups. Thealkyl groups more preferred are those with a secondary carbon in thealpha position to the nitrogen. In this configuration, the antiozonantactivity of the compound is believed to be enhanced. Therefore, the morepreferred alkyl groups are branched chains which provide an alkylsubstituent which is in accordance with this configuration. Thecycloalkyl or C₁ -C₁₂ alkyl substituted cycloalkyls provide such analpha carbon configuration as well. The structure of formula I which ismost preferred at this time are compounds in which R¹, R² and R³ are C₆-C₈ branched chain alkyl groups. Examples of some preferred startingtriazines of the present invention are:2,4,6-tris(N-1,4-dimethylpentyl-p-phenylenediamino)-1,3,5 -triazine;2,4,6-tris(N-isopropyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris(N-cyclohexyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris(N-sec-butyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris(N-1,3-dimethylbutyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris (N-1- methylheptyl-p-phenylenediamino)-1,3,5- triazine;2,4,6-tris(N-2,4-di-tert-butylcyclohexyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris(N-2-sec-butylcyclohexyl-p-phenylenediamino)-1,3,5-triazine;2,4,6-tris(1-methyldecyl-p-phenylenediamino)-1,3,5-triazine. The mostpreferred material2,4,6-tris(N-1,4-dimethylpentyl-p-phenylenediamino)-1,3,5-triazine.

The preferred compounds of this invention are the mono or bis or trisquinone diimines or mixtures of the foregoing materials. As shown instructure (I), the nomenclature for the mono, bis and tris materials is:

Mono quinonediimino triazine--

2,4-bis(N-1,4alkyl-p-phenylenediamino)-6-(N-1,4-alkyl-p-quinonediimino)-1,3,5triazine;

Bis quinonediimino triazine--

2-(N-1,4 alkyl-p-phenylenediamino)-4,6-bis(N-1,4-alkyl-p-quinonediimino)-1,3,5 triazine;

Tris quinonediimino triazine--

2,4,6-tris(N-1,4 alkyl-p-quinonediimino)-1,3,5-triazine.

The compounds of the invention can be synthesized advantagously by thefollowing general method. Although the reagents may be added indifferent order as shown in some of the examples, the preferred methodfor preparation of the triazine intermediate is as follows:

The N-alkyl-p-phenylenediamine, which is prepared by methods known tothose familiar with the art, is reacted with2,4,6-tri-halogeno-1,3,5-triazine. A molar equivalent of the preferredtri-halo triazine commonly called cyanuric chloride is added as a powderto a solution of three plus moles of the N-alkyl-p-phenylenediamine in asuitable solvent such as isopropanol, at ambient temperatures withappropriate cooling. The first two halogen atoms are displaced rapidly.The reaction mixture is then heated to 60°-80° C. in order to completethe displacement of the third halogen atom. After 4-5 hours heating at60°-80° C. the formation of the2,4,6-tris-(N-alkyl-p-phenylenediamino)-1,3,5-triazine trihydrochlorideis complete.

The process is unique in that the basicity of thealkyl-p-phenylenediamine allows the displaced halogen atom of thecyanuric halide to form the hydrohalide directly thereby enablingisolation of the trihalide and effecting a purification step.

The tris-hydrochloride may be removed by filtration, then reslurried ina suitable water miscible solvent, neutralized with aqueous base such assodium hydroxide, and crystallized from the aqueous solvent mixture.

If the starting N-alkyl-p-phenylenediamine is sufficiently pure, or aless pure product is acceptable, isolation of the tris-hydrochloride isnot necessary, and the reaction mixture can be neutralized and theproduct crystallized and isolated by filtration.

Temperature control of the reaction is of some importance. It ispreferred that the first stage of the reaction take place below 30° C.and that the second stage take place at least 30° C. above the firststage. Selection of the optimal temperatures are, of course, dependentupon the identity of the p-phenylenediamine and solvent which is chosen.

Preferred solvents are alcohols although any suitable solvent may beutilized. The term solvent is meant to include an excess of theN-alkyl-p-phenylenediamine which may serve to solvate the reactionproduct and allow subsequent isolation.

The critical oxidation step may be carried out on the reaction mixtureeither after neutralization, after crystallization or after filtration.A preferred method is described below where the pure2,4,6-tris(N-alkyl-p-phenylenediamino)1,3,5-triazine is redissolved andthen oxidized. The oxidizing agent may be any known oxidant, which isneutral or basic in nature. In the process described below, theoxidizing agent is one which is preferentially soluble in an aqueousmedium to simplify isolation of the final product.

The oxidation step preferably takes place in the presence of polarsolvent(s) with an optional nonpolar cosolvent.

EXAMPLE 1 Preparation of a Mixture of Mono- and Bis-Quinonediiminesderived from 2,4,6-tris(N-1,4dimethylpentyl-p-phenylene-diamino)1,3,5-triazine

The triazine (0.01 moles) was dissolved in a 1:1 mixture of acetonitrileand toluene. After adjusting the temperature to 25°-30° C., 0.02 molesof a 10-12% aqueous solution of sodium hypochlorite was added dropwiseover 10-15 minutes. The mixture was stirred vigorously for two hours.The reaction mixture was quenched in water and the organic layercontaining the product was separated. The solvent was removed bydistillation under vacuum and the crude product mixture was recovered asa resinous solid. The assay of the material by high pressure liquidchromotography showed. 6% Tris, 60% Bis, 31% Mono and 3% startingtriazine.

EXAMPLE 2 Preparation of a Mixture of Bis- and Tris-Quinonediiminesderived from2,4,6-tris(N-dimethylpentyl-p-phenylenediamino)-1,3,5-triazines

The same procedure was used as above except that 3 equivalents of sodiumhypochlorite were used per equivalent of the triazine. Work up of theproduct gave material having the following assay: 50% Tris, 43% Bis, 6%Mono, and less than 1% of the starting triazine.

Mono quinonediimino triazine--

2,4-bis(N-1,4dimethylpentyl-p-phenylenediamino)-6-(N-1,4-dimethylpentyl-p-quinonediimino)-1,3,5triazine.

Bis quinonediiminotriazine--

2-(N-1,4-dimethylpentyl-p-phenylenediamino)-4,6-bis(N-1,4-dimethylpentyl-p-quinonediimino)-1,3,5triazine.

Tris quinonediimino triazine--

2,4,6-tris(N-1,4-dimethyl-pentyl-p-quinonediimino)-1,3,5-triazine.

The respective molecular weights by tandem mass spectroscopy were 692,690; 688 respectively.

The general synthesis method follows the procedures above bysubstituting the appropriate 2,4,6-tris(N-alkyl-p-phenylenediamino)-1,3,5-triazine as the starting material. The oxizing agent maybe changed to suit the physical form of the triazine starting material,solvents and cosolvents, reaction temperatures and desired isolation andpurification procedures.

COMPARATIVE EXAMPLE A Synthesis of Triazine Intermediates EXAMPLE 1:2,4,6-tris(N-1,4-dimethylpentyl-p-phenylene diamino)-1,3,5-triazine

In a 3-liter, four-necked, round-bottomed flask equipped with athermometer, a mechanical stirrer, a condenser, and a dropping funnelwas placed 1500 ml of isopropanol. The ispropanol was cooled to -10° C.and 184.4 grams (1 mole) of cyanuric chloride was added. To this stirredsuspension was added 680 grams (3.3 moles) of 4-amino-N-(1,4dimethylpentyl)aniline dropwise over 1 hour period keeping thetemperature between -10° and -5° C. Over 1 hour the reaction mixture waswarmed to 30° C. then held for 16 hours at 30° C. The reaction mixturewas refluxed for 1 hour at about 80° C. The reaction was followed byhigh pressure liquid chromatograph by observing the disappearance of thestarting amine, and the conversion of the intermediate mono- andbis-substituted compounds to the final tris-substituted product. Aftercooling to 60° C. 240 grams (3 moles) of 50 percent sodium hydroxidesolution was added dropwise over 1 hour period. The sodium chloride wasremoved by filtration at 40° C. The filtrate was cooled to 10° C. andthe solvent was decanted off. The oily lower layer was extracted withwater at 60° C. then crystallized from fresh isopropanol. The titlecompound was recrystallized from hexane and it melted at 128°-132° C.The yield was 78.1 percent. The infrared spectrum was consistent withthe structure. Relative area HPLC analysis of the product showed it tobe 95.8 percent pure.

The compounds of the invention are most advantagously utilized asantiozonants to protect blends of highly unsaturated polymers such asnatural or synthetic elastomers. Representative of the highlyunsaturated polymers which may be employed in the practice of thisinvention are diene elastomers. Such elastomers will typically possessan iodine number of between about 100 and about 250, although highlyunsaturated rubbers having a higher or a lower (i.e., of 50-100) iodinenumber may also be employed. Illustrative of the diene elastomers whichmay be utilized are polymers based on conjugated dienes such as1,3-butadiene; 2-methyl-1,3-butadiene; 1,3-pentadiene; 2 chloro-1,3butadiene, 2,3-dimethyl-1, 3-butadiene; and the like, as well ascopolymers of such conjugated dienes with monomers such as styrene,alpha-methylstyrene, acrylonitrile, methacrylonitrile, methyl acrylate,ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetateand the like. Preferred highly unsaturated rubbers include naturalrubber, cis-polyisoprene, polybutadiene, poly(styrene-butadiene),polychloroprene and poly(acrylonitrile-butadiene). Moreover, mixtures oftwo or more highly unsaturated rubbers may be employed. Also, mixturesof the highly unsaturated rubbers with elastomers having lesserunsaturation such as EPDM (ethylene-propylene-diene rubber), EPR(ethylene propylene rubber), butyl or halogenated butyl rubbers are mostpreferred in this invention.

The novel compounds of the invention may be used in combination withother antiozonants such as the triazines of U.S. Pat. No. 4,794,134 andless preferably with microcrystalline waxes as are commonly used toprotect against static ozone attack. The other antiozonants which may beutilized include any of the commonly recognized paraphenylenediamineclass of materials:

N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine;

N-phenyl-N'-isopropyl-p-phenylenediamine;

N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine;

N-phenyl-N'-cyclohexyl-p-phenylenediamine; mixeddiaryl-p-phenylenediamines;

N,N'-diphenyl-p-phenylenediamine;

N,N'-di-beta-naphthyl-p-phenylenediamine;

N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine;

N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine;

N,N'-bis(1-methylheptyl)-p-phenylenediamine;

N-phenyl-N'-p-toluenesulfonyl-p-phenylenediamine;

N-phenyl-N'-alkyl-p-phenylenediamine;

6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline; and nickel dibutyldithiocarbamate.

The highly unsaturated polymers to be protected may be formulated inconventional manner with the many usual compounding ingredients, forexample, vulcanizing agents, accelerators, activators, retarders,antiozonants, antioxidants, plasticizing oils and softeners, fillers,reinforcing pigments and carbon blacks.

The novel compounds of the invention may be added to an unsaturatedpolymer at a level of from 0.1 to about 10 parts by weight per hundredparts by weight of rubber hydrocarbon (hereinafter PHR). For thesepurposes the polymer is assumed to be a natural or synthetic rubber. Amore preferred addition level is about 1 to about 8 parts PHR. The mostpreferred level is from about 2 to about 6 parts PHR. When thequinonediimino triazine compounds of the invention are used incombination with other antiozonants such as the paraphenylenediamineclass of materials, they may be added in a blend which totals to theranges set forth above. The compounds of the invention may be blendedwith the other antiozonants at ratios ranging from 1:3 to 3:1. Morepreferred is a ratio range of 2:3 to 3:2. These ratios are meant toindicate the percentages are 40:60 to 60:40 where in all cases thetriazine compounds of the invention are the first number of each ratio.It should be noted that in certain applications and with certain otherantiozonants, the PHR ranges of antiozonant listed above may be variedin order to obtain the optimal protection. Reasonable experimentationmust be undertaken in order to optimize the ratios and overall levels ofthe blend when the triazine compounds of the invention are blended withother conventional antioxidants and antiozonants.

ANTIOZONANT UTILITY EXAMPLES 9-24

The quinone diimine derivatives of N-alkylarylenediamino triazinecompounds of the invention function as outstanding antiozonants inrubber polymers with no migratory staining tendency evident at thistime. The following examples demonstrate their utility in a variety ofozone and color stability test regimes. All tests utilize the triazinesin vulcanized rubber compounds as are typical in the industry. Thefollowing test formulation is a typical rubber compound.

    ______________________________________                                        TEST FORMULATION                                                                               Parts by Weight                                              ______________________________________                                        Natural Rubber (SMR5CV)                                                                          50.0                                                       Polybutadiene (cis 1,4 BR)                                                                       50.0                                                       Carbon Black (N-660)                                                                             50.0                                                       Zinc Oxide         3.0                                                        Stearic Acid       1.0                                                        Aromatic Oil       10.0                                                       Benzothiazole Sulfenamide                                                                        1.0                                                        Sulfur (20% oil)   2.0                                                        Antiozonant - Variable                                                                           4.0                                                        ______________________________________                                    

The foregoing test formulation was used for all test samples unlessotherwise noted. The formulation is an approximation of a typical tiresidewall compound. The identity and level of the antiozonant are thevariables to be evaluated in the subsequent examples.

The test formulation was utilized to make uncured test sheets bypreblending the natural rubber and polybutadiene. Once blending wasaccomplished, all other ingredients except the sulfur and benzothiazolesulfenamide were added to form a nonproductive compound and in asubsequent mixing step, the foregoing ingredients were added. Testssheets for the subsequent testing were cured in a platen press betweenheated plates for a time sufficient to achieve full cure. For thepurposes of testing, a fifteen minute cure at 160° C. was normallyutilized. The exact sample configuration of the test specimens for theozone testing varies by the description of the ASTM method utilized.Reference is made to the ASTM test methods and such methods areincorporated herein by reference to abbreviate the required descriptiveinformation regarding specimen preparation, test methods and testresults.

OZONE TEST RESULTS

Ozone testing was conducted utilizing the standard test method of ASTMD1149-81 which is titled Rubber Deterioration - Surface Zone Cracking ina Chamber (Flat Specimen). This method covers the estimation of theresistance of vulcanized rubber to cracking when exposed to anatmosphere containing ozone. Rubber specimens are kept under a surfacetensile strain and the ozone content in the test chamber is maintainedat a 50 part per hundred million level (mPa) in a 100° F. (38° C.) testchamber. A common designation for this test is the bent loop test methodsince the test specimen is placed under strain by having it clamped in alooped configuration in which varying degrees of strain and elongationresult. This bent loop configuration is an extremely severe testconfiguration in which failure can be expected in a relatively few hoursgiven the high temperature and high ozone atmosphere in which the testsamples are placed.

                  TABLE 1                                                         ______________________________________                                                   Blank Comparative A                                                                             Ex 1    Ex 2                                     ______________________________________                                        Dynamic Ozone                                                                              Crack   Pass        Pass  Pass                                   96 Hrs @ 38° C.                                                        50 (mPa)                                                                      Bloom        None    Yellow      Black Black                                  Unaged                                                                        Aged 3 days @                                                                              Brown   Black       None  NT                                     100° C.                                                                Outdoor Aging                                                                              Fail    Pass        Pass  Pass                                   Lacquer                                                                       Staining Test*                                                                             +       0           +     +                                      ASTM-D 925-83(C)*                                                             ______________________________________                                         *Comparative A was used as the standard                                       + is better than standard                                                     NT = Not Tested                                                          

Table 1 summarizes a series of antiozonant screening tests. Thecompounds of the invention (Examples 1 and 2) demonstrated excellentozone protection, outdoor aging and staining characteristics. Thetendency to bloom or discolor the surface of the rubber stock isimproved over the yellow bloom of Comparative A. It should be noted thatif a conventional paraphenylenediamine antiozonant [standard in tireindustry] had been included in this series, it would have demonstrated avery high intensity brown bloom and severe staining characteristics inthe lacquer test.

Industrial Applicability

The compounds of this invention are materials which are ideally suitedfor use as antiozonants in tire sidewalls, carcass and treadcompositions. The excellent ozone resistance and non-stainingcharacteristic is highly desirable in tire and rubber product. The factthat when blooming to the surface does occur it takes the form of adesirable flat black appearance which is invisible on the tire surfacemakes these materials more unique and desirable. This unique combinationof characteristics sets these materials apart from all of theantiozonants of the prior art.

The quinone diimine derivatives of2,4,6-tris(N-alkyl-p-phenylenediamino)-1,3,5-triazines can be mostadvantageously used in a tire as a component of any or all of thethermosetting rubber-containing portions of the tire. These include thetread, sidewall and carcass portions of a truck, passenger or off-roadvehicle tire which also contain many different reinforcing layerstherein. These components typically contain more than one thermosettingrubber polymer in a blend which must be protected from ozonedegradation, as well as oxidative attack. Methods of incorporating thesecompounds into the tire are conventional and well known.

In view of the many changes and modifications that may be made withoutdeparting from principles underlying the invention, reference should bemade to the appended claims for an understanding of the scope of theprotection afforded the invention.

What is claimed is:
 1. A degradation-resistant composition comprising:anunsaturated polymer having homogeneously incorporated therein aneffective amount of one or more compounds of the general formula:##STR3## Y and Z are independently selected from ##STR4## in which R¹,R² and R³ are radicals independently selected from a C₃ -C₁₈ branched orlinear alkyl, or a C₃ -C₁₂ cycloalkyl or a C₃ -C₁₂ cycloalkylsubstituted with one or more C₁ -C₁₂ alkyl groups.
 2. A tire having anelastomeric body including carcass, tread and sidewall portions, saidelastomeric body comprising:a plurality of thermosetting rubber polymerstherein; and a plurality of reinforcing materials positioned within saidbody, at least one of said plurality of thermosetting rubber polymershaving dispersed therein an antidegradant composition composed of one ormore compounds of the general formula: ##STR5## Y and Z areindependently selected from ##STR6## in which R¹, R² and R³ are radicalsindependently selected from a C₃ -C₁₈ branched or linear alkyl, or a C₃-C₁₂ cycloalkyl or a C₃ -C₁₂ cycloalkyl substituted with one or more C₁-C₁₂ alkyl groups.